Millions of people worldwide are afflicted by irreversible vision loss attributed to glaucoma. Over 3 million Americans are estimated to have glaucoma and approximately 120,000 are blind because of this disease.
There are often no signs or symptoms until vision loss is severe; estimates indicate that only half of the 3 million Americans with glaucoma are aware they have the disease. The cause of the disease is not well understood and there is currently no cure. Glaucoma is a chronic disease and must be treated for life.
Glaucoma is characterized by vision loss due to the damage of the optic nerve. Specifically, glaucoma is characterized by pathological changes in the optic disc and nerve fiber layer of retina.
One mechanism that can lead to damage of the optic nerve is the development of high intraocular pressure (IOP). Evidence from large, prospective studies suggests that reducing IOP to normal levels (15.5±2.6 mmHg (mean±SD)) reduces the rate of disease progression. Examples of such studies include Ethier et al., “Ocular biomechanics and biotransport,” Annu Rev Biomed Eng, Vol. 6, pp. 249-73 (2004), and Schwartz and Budenz, “Current management of glaucoma,” Curr Opin Ophthalmol, Vol. 15, pp. 119-26 (2004), both of which are incorporated by reference herein for all purposes.
Glaucoma management options include medical therapy, laser surgery, incisional surgery, and glaucoma drainage devices (GDDs). Medical therapy lowers IOP by improving the outflow of aqueous humor (AH) or to reduce its production. Some surgical techniques attempt to stimulate AH outflow, however, the primary surgical strategy is to manage glaucoma by lowering the patients' IOP through removal of excess AH. Regardless of the technique that is employed, accurate real-time measurements of IOP and the ability to restore normal levels are critical in the treatment of this disease.
Glaucoma management typically starts from interventions that are the safest and least invasive. Inasmuch, medical therapy is the most widely used treatment initially.
Although incurable, glaucoma can be treated with the aid of implant technology. Specifically, GDDs are used as a last resort in cases of refractory glaucoma or in patients who have not responded to previous treatment attempts. While GDDs can potentially lower IOP effectively, ophthalmologists are reluctant to use current GDDs due to high rates of complications.
Modern GDDs are based on the 1969 concept of the Molteno implant which consists of tube that shunts aqueous humor from anterior chamber to an external subconjunctival plate. Incorporated by reference herein for all purposes is Molteno, “New implant for drainage in glaucoma. Clinical trial,” Br J Ophthalmol, vol. 53, pp. 606-15, (1969).
In the last 30-40 years, few innovative advances in surgical operation or implant devices have occurred. Only two major modifications to GDDs have been introduced: (1) addition of a valve to resist outflow and reduce hypotony and (2) increase in the endplate surface area to achieve lower IOPs.
GDDs are currently limited to the treatment of refractory glaucoma due to complications. The most significant complication of GDDs is postoperative hypotony (a condition where IOP is abnormally low, IOP<5 mmHg). During the early postoperative period, there is a lack of flow resistance prior to fibrous capsule formation around the end-plate resulting in hypotony, flat anterior chambers, choroidal effusions, and suprachoroidal hemorrhages. Strategies to avoid hypotony include performing the operation in two-stages to allow fibrous capsule formation, tube ligature, internal tube occlusion, and the development of valved GDDs. These solutions are not ideal and interestingly, conventional valved implants do not eliminate the occurrence of these complications. Furthermore, the success rate of current GDDs decreases by 10-15% every year suggesting poor long term performance.
Accordingly, improved devices and methods for treating glaucoma are highly desirable.